In vitro contractility of stimulated and non-stimulated human gallbladder muscle

In an attempt to define, more clearly, the nature of gallbladder contraction we obtained muscle strips from human gallbladder wall, removed at cholecystectomy. Samples were taken from various areas of the gallbladder to seek evidence of a dominant axis of contraction. The strips were stimulated with increasing concentrations of cholecystokinin-8 (CCK-8) and carbachol, and, to determine maximal contractile force, 0.25 M potassium chloride. No differences were seen between samples taken from the longitudinal, circular and oblique axes. In a second series of experiments, samples were taken from the body and neck regions of the gallbladder. In these, it was seen that the samples from the body contracted more forcefully than those of the neck tissue and that they were more sensitive to carbachol stimulation. The difference in response to CCK-8 measured in the strips from the body and cystic duct/neck of the gallbladder cannot be explained by a difference in sensitivity to CCK-8, but is mainly due to the difference in the amount of muscle tissue present. Strips from the body are more sensitive to muscarinic stimulation that those from the neck. Overall, there is a functional difference in sensitivity between the body and neck which would serve to facilitate bile flow into the common bile duct during gallbladder contraction.